Firstly it should be as individual as possible , you don't want the same old shit every Joe Bloggs has done.
Secondly it should be something that 20 years from now you still won't mind looking at ( I have tats dating back to 1979) .
Finaly if you can't decide then it's generaly best to wait till you're certain of what you want and where you want it.

I know lots of people with music related tats who can't play a note so that shouldn't really be a concern.
My own personal taste in music is very varied and I never rush into making a choice , I decided (after a very long time) to go with my favourite type of music which is Psychobilly.
My fave group are The Cramps so I decided to "steal" one of thier album covers.

The original pic had the name of the band through the hair but I decided I didn't want that.